Hi Roger,
I hope this website may help you.
http://www.tb-kumano.jp/en/kumano-kodo/
Yes, they have Dual Pilgrim passport, Camino de Santiago and Kumano Kodo.
Buen Camino !
Takako
This site is run by Ivar at in Santiago de Compostela.
This site participates in the Amazon Affiliate program, designed to provide a means for Ivar to earn fees by linking to Amazon